First observation of Raphidiopsis (Cylindrospermopsis) raciborskii (Nostocales) during a heatwave in Lake Comabbio (Northern Italy)

In July 2015, the first documented observation of the freshwater cyanobacterium Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) in Lake Comabbio, Northern Italy, was reported. This species, known for its potential toxicity and invasive nature, had previously been observed in Central Italy and Sardinia. It produces harmful toxins such as cylindrospermopsin and saxitoxins, which can bioaccumulate in aquatic life and pose significant risks to both animals and humans. The heatwave in 2015, with record high temperatures, created favourable conditions for the bloom. The cyanobacterium was present in high concentrations, dominating the phytoplankton community, with saxitoxin levels detected in lake samples. Satellite data confirmed high chlorophyll-a concentrations and elevated water temperatures. This emerging threat highlights the need for enhanced monitoring and public awareness regarding the risks posed by harmful cyanobacteria.